Roller mill

ABSTRACT

A side feed type of roller mill having a housing, a rotating table provided in the housing, and a feed inlet chute extending obliquely downwardly through an upper side wall of the housing and having a lower end exposed over the rotating table. The feed inlet chute includes a cylindrical chute body and a liner mounted inside the chute body. The liner is formed of a flexible elastic material, so that the inner surface of the liner is irregularly deformed as accompanying peristalsis and vibration by both the own weight and the gliding/falling forces of a feed material passing through the chute and the elastic restoring force of the liner itself. Accordingly, a deposit layer of the feed material formed on the inner surface of the liner can soon be autonomously removed by the deformation of the liner without interruption of the operation of the roller mill. Thus, stable and efficient pulverization can be continuously performed.

BACKGROUND OF THE INVENTION

The present invention relates to a roller mill for pulverizing a feedmaterial such as granulated slag, cement material, cement clinker,gypsum, or coal, and more particularly to a roller mill having a sidefeed type of feed inlet chute.

There are various types of pulverizers for pulverizing a feed materialsuch as granulated slag, cement material, cement clinker, gypsum, orcoal. Of the known various types of pulverizers, a roller mill has beenwidely used in recent years because of its pulverizing efficiencysuperior to that of a ball mill. While various types of roller millsexist, they are generally classified into a center feed type and a sidefeed type from the viewpoint of arrangement of a feed inlet chute.

An example of the center feed type of roller mill is shown in FIG. 7 invertical section. As shown in FIG. 7, a feed inlet chute 70 extendsvertically through an upper central portion of a housing 1. A feedmaterial is supplied through the feed inlet chute 70 forming a verticalpassage onto a rotating table 4 along its vertical axis of rotation.

On the other hand, an example of the side feed type of roller mill isshown in FIG. 8A in vertical section. As shown in FIG. 8A, a feed inletchute 80 extends obliquely downwardly through an upper side wall of ahousing 1 in such a manner that the lower end of the feed inlet chute 80is exposed over a rotating table 4. A feed material is supplied throughthe feed inlet chute 80 forming an inclined passage onto the rotatingtable 4 along a line intersecting its vertical axis of rotation.

The general operation of these types of roller mills will be describedwith reference to FIGS. 7 and 8A. A feed material is supplied throughthe feed inlet chute 70 or 80 onto the rotating table 4 which is rotatedabout its vertical axis of rotation by a speed reducer 3 driven by amotor 2. The feed material supplied onto the rotating table 4 is movedto an outer peripheral portion of the rotating table 4 by a centrifugalforce generated by the rotation of the rotating table 4. The feedmaterial moved to the outer peripheral portion of the rotating table 4is pulverized by a plurality of pulverizing rollers 5 rotating inpressure contact with the upper surface of the rotating table 4 at theouter peripheral portion thereof. Each pulverizing roller 5 is pressedon the upper surface of the rotating table 4 by a hydraulic cylinder 7through a swing arm 6.

The feed material thus pulverized is raised by a heated gas flowinjected from a plurality of injection nozzles 8 provided around therotating table 4, and is then selectively separated by a separator 9provided at an upper portion in the casing 1, so that fine powder havinga given size or less obtained by pulverizing the feed material isallowed to pass through the separator 9 and is then ejected from anoutlet opening 1a formed at an upper side portion of the casing 1. Onthe other hand, relatively coarse powder not allowed to pass through theseparator 9 falls on the rotating table 4, and is subjected topulverization again.

In general, however, the feed material to be pulverized by the rollermill mostly contains fine powder having a high viscosity, and sometimescontains moisture as in granulated slag. Accordingly, such fine powderof the feed material is deposited on the inner surface of the feed inletchute during passage through the chute, resulting in the formation of adeposited layer of the fine powder strongly sticking to the innersurface of the chute. If this deposit layer is allowed to accumulate, itgrows to narrow the passage of the chute through which the feed materialcan pass. As a result, normal supply of the feed material into theroller mill is hindered by the growth of the deposit layer. Finally, thepassage of the chute is choked by the deposit layer resulting in thefatal condition that the feed material can no longer be supplied intothe roller mill.

To cope with this problem, various cleaning devices for removing thedeposit layer formed on the inner surface of the feed inlet chute at asuitable time have been proposed especially for the center feed type ofroller mill. For example, there has been proposed in Japanese PatentLaid-open Publication Nos. 4-145958, 4-176344, and 4-200656 a cleaningdevice having a jig adapted to be moved vertically inside the verticalfeed inlet chute for scraping off the deposit layer.

In the center feed type of roller mill, the feed inlet chute isvertically provided at the top of the housing of the roller mill.Accordingly, auxiliary facilities for carrying the feed material to ahigh position over the top of the housing become large in size. Further,it is necessary to concentrically arrange the feed inlet chute and theseparator. Thus, the roller mill as a whole becomes very complicated instructure with the disadvantages such that the manufacturing cost forthe roller mill as a whole, the number of man-hours for the checking andreplacement of the feed inlet chute, etc. are high compared to those forthe side feed type of roller mill.

The above-mentioned cleaning devices for the center feed type of rollermill as conventionally proposed have the following problems.

In the cleaning device described in Japanese Patent Laid-openPublication No. 4-145958, it is necessary to detach and attach thecleaning device every time the cleaning of the feed inlet chute iscarried out. Further, in detaching and attaching the cleaning device andin actually cleaning the feed inlet chute, the operation of the rollermill must be stopped.

In the cleaning device described in Japanese Patent Laid-openPublication No. 4-176344, the cleaning device is always installed in thefeed inlet chute in such a manner as not to hinder the pass of a feedmaterial through the chute. Accordingly, it is unnecessary to detach andattach the cleaning device in carrying out the cleaning of the chute,and the chute can be cleaned without stopping the operation of theroller mill. However, when the chute is cleaned by the cleaning device,the fine powder of the feed material is deposited to the cleaningdevice, so that it is necessary to clean the cleaning device itself andstop the operation of the roller mill when carrying out the cleaning ofthe cleaning device. Further, the cleaning device cannot be storedoutside the feed inlet chute during the operation of the roller mill. Asa result, the cleaning device is always exposed to a flow of feedmaterial in the chute, thus promoting the deposition of the feedmaterial to the cleaning device.

In the cleaning device described in Japanese Patent Laid-openPublication No. 4-200656, the feed material chute has a two-waystructure to form a space through which a feed material does not pass,so that the cleaning device is stored in this space at any time otherthan during the cleaning of the feed inlet chute, thereby greatlysolving the above problem. However, there still remains the problem thatthe operation of the roller mill must be stopped when cleaning thecleaning device after the feed inlet chute has been cleaned by thecleaning device.

On the other hand, in the side feed type of roller mill, the depositionof a feed material on the inner surface of the feed inlet chute occursmore readily than that in the center feed type of roller mill, becausethe feed inlet chute is inclined. Further, since the feed materialglides and falls along a circumferential bottom portion of the innersurface of the chute, the circumferential bottom portion in particularis prone to be partially worn.

To suppress the deposition of the feed material, an inclination angle ofthe feed inlet chute is set to be high in the conventional side feedtype of roller mill. However, the enlargement of the inclination angleof the chute causes the problem that the lower end of the chute does notextend to the central portion of the roller mill. As a result, the feedmaterial cannot be dropped on the center of the rotating table thuscausing nonuniform supply of the feed material to each pulverizingroller, thus reducing the pulverizing efficiency.

As shown in FIG. 8B which is a cross section taken along the line A--Ain FIG. 8A, the partial wear of the circumferential bottom portion ofthe inner surface of the chute as mentioned above can be prevented bymounting a liner 81 on the inner surface of the feed inlet chute 80 at aU-shaped bottom portion thereof. However, since the liner 81 is formedof ceramics having a high wear resistance or sheet steel with specialhard facing, the manufacturing cost of the liner 81 is relatively high.

SUMMARY OF THE INVENTION

It is accordingly an object of the present invention to provide a rollermill having a side feed type of feed inlet chute which can bemanufactured at low costs.

It is another object of the present invention to provide a roller millhaving a side feed type of feed inlet chute which can easily andsecurely remove the deposit layer formed on the inner surface of thechute without interruption of operation of the roller mill.

It is a further object of the present invention to provide a roller millhaving a side feed type of feed inlet chute which can stably supply afeed material over the central portion of the rotating table in theroller mill.

It is a still further object of the present invention to provide aroller mill having a side feed type of feed inlet chute which cancontinuously perform stable and efficient pulverization to therebyimprove productivity.

According to the present invention, there is provided in a roller millhaving a housing, a milling table adapted to be rotated about a verticalaxis provided in said housing, a plurality of milling rollers providedin said housing and mounted so as to act against an outer portion of theupper surface of said milling table and a feed inlet chute extendingobliquely through a side wall of said housing for supplying a feedmaterial from outside the housing onto said milling table to bepulverized between said milling table and said milling rollers; whereinsaid feed inlet chute comprises a liner made of a flexible elasticmaterial which is preferably mounted inside a chute body.

The liner may be mounted through a plurality of spacers to the chutebody, so that a space is defined between the liner and the chute body.

The chute body may have means for forcibly deforming the liner.

The chute body may have liner deforming means adapted to be operated bya command from an external control unit to forcibly deform the liner andpressure detecting means for detecting pressure in the chute body totransmit the pressure detected to the external control unit.

Further, the chute body may have means for cooling the liner.

In the roller mill of the present invention, the feed inlet chuteextending obliquely downwardly through the upper side wall of thehousing and having the lower end exposed over the rotating tableincludes the cylindrical chute body and the liner mounted inside thechute body, and the liner is formed of a flexible elastic material.Accordingly, when a feed material is discharged into the feed inletchute, the liner having a flexibility and elasticity is elasticallydeformed by weight and the gliding/falling forces of the feed materialpassing through the chute. The liner thus elastically deformed restoresits original form through an elastic restoring force. Therefore, theinner surface of the liner generates irregular deformation accompanyingperistalsis and vibration due to both the weight and the gliding/fallingforces of the feed material and the elastic restoring force of theliner. Accordingly, even when a deposit layer of the feed material isformed on the inner surface of the liner of the chute, the deposit layercan soon be removed by the irregular deformation of the inner surface ofthe liner caused by the passage of the feed material through the chute,thus preventing the growth of the deposit layer.

In this manner, the removal of the deposit layer formed in the feedinlet chute can be autonomously attained by the deformation of the linercaused by the passage of the feed material through the feed inlet chuteduring the operation of the roller mill. Therefore, the removal of thedeposit layer does not depend on a cleaner or the like moving in a feedinlet chute as in the conventional roller mill. Further, it isunnecessary to interrupt the operation of the roller mill, so as toperform the removal of the deposit layer. Thus, the growth of thedeposit layer in the feed inlet chute can be prevented to make thepassage of the feed material smooth and stable. Further, it isunnecessary to unduly largely incline the feed inlet chute for thepurpose of suppressing the deposition of the feed material, and aninclination angle suitable for supplying the feed material to thecentral portion of the rotating table can be selected, thereby effectingefficient pulverization.

In the case where the liner is mounted through a plurality of spacers tothe chute body, thereby defining a space between the liner and the chutebody, the liner can be flexed by the weight and the gliding/fallingforces of the feed material passing through the chute, therebygenerating a larger deformation of the inner surface of the liner.Accordingly, the deposit layer on the inner surface of the liner can beremoved more securely.

In the case where the chute body has means for forcibly deforming theliner, the liner can be deformed not only by the weight and thegliding/falling forces of the feed material, but also forcibly by theliner deforming means. Accordingly, the deposit layer on the innersurface of the liner can be removed more securely and easily.

The roller mill is usually operated in the condition where the inside ofthe housing is kept under a negative pressure or a positive pressurewith respect to atmospheric pressure. Accordingly, when the depositionof the feed material on the inner surface of the feed inlet chute causesa reduction in sectional area of the passage of the chute, there resultsa difference in pressures between the upper and lower end portions ofthe chute body. Accordingly, in the case where the chute body has meansadapted to be operated by a command from an external control unit toforcibly deform the liner and means for detecting pressure in the chutebody to transmit the pressure detected to the external control unit, achange in pressure in the chute body is transmitted to the externalcontrol unit, and the liner deforming means is operated according to thechange in pressure, thereby always maintaining a good condition wherethe growth of the deposit layer on the inner surface of the liner iseliminated.

Further, in the case where the chute body has means for cooling theliner, a temperature rise of the liner due to hot air introduced intothe roller mill can be suppressed to thereby prevent materialdeterioration of the liner due to any temperature rise.

Other objects and features of the invention will be more fullyunderstood from the following detailed description and appended claimswhen taken with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a vertical sectional view of a roller mill according to afirst preferred embodiment of the present invention;

Fig. 1B is a cross section taken along the line A--A in FIG. 1A;

FIG. 1C is a cross section taken along the line B--B in FIG. 1A;

FIG. 2A is a vertical sectional view of an essential part of a rollermill according to a second preferred embodiment of the presentinvention;

FIG. 2B is a cross section taken along the line A--A in FIG. 2A;

FIG. 2C is a cross section taken along the line B--B in FIG. 2A;

FIG. 3A is a vertical sectional view of an essential part of a rollermill according to a third preferred embodiment of the present invention;

FIG. 3B is a cross section taken along the line A--A in FIG. 3A;

FIG. 4A is a vertical sectional view of an essential part of a rollermill according to a fourth preferred embodiment of the presentinvention;

FIG. 4B is a cross section taken along the line A--A in FIG. 4A;

FIG. 5 is a vertical sectional view of an essential part of a rollermill and an operation control system therefor according to a fifthpreferred embodiment of the present invention;

FIG. 6 is a vertical sectional view of an essential part of a rollermill and an operation control system therefor according to a sixthpreferred embodiment of the present invention;

FIG. 7 is a vertical sectional view of a center feed type of roller millin the prior art;

FIG. 8A is a vertical sectional view of a side feed type of roller millin the prior art; and

FIG. 8B is a cross section taken along the line A--A in FIG. 8A.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A first preferred embodiment of the present invention will now bedescribed with reference to FIGS. 1A to 1C, wherein FIG. 1A is avertical sectional view of a roller mill as a whole; FIG. 1B is a crosssection taken along the line A--A in FIG. 1A; and FIG. 1C is a crosssection taken along the line B--B in FIG. 1A. In FIGS. 1A to 1C, thesame reference numerals as those shown in FIGS. 8A and 8B denote thesame parts, and the explanation thereof will be omitted hereinafter.

Referring to FIGS. 1A to 1C, reference numeral 10 denotes a feed inletchute. The feed inlet chute 10 is of a side feed type such that isincludes a cylindrical chute body 11 passing obliquely downwardlythrough an upper side wall of a housing 1 and having a lower end exposedover a central portion of a rotating table 4, and also includes liners12 and 12' mounted on the inner surface of the chute body 11. The chutebody 11 is formed of sheet steel, and the liners 12 and 12' are formedof sheet rubber. Although not shown, an air seal mechanism formaintaining a negative pressure in the roller mill is connected to theupper end of the feed inlet chute 10.

The chute body 11 is composed of a relatively long inclined portion 11aand a relatively short upright portion 11b continuously connected to theupper end of the inclined portion 11a. As apparent from FIG. 1B, theinclined portion 11a has a U-shaped cross section such that the top sideis formed as a flat lid and the bottom side is curved to form an arcshape. The inclined portion 11a passes through the upper side wall ofthe housing 1, and is detachably mounted thereto. As apparent from FIG.1C, the upright portion 11b has a circular cross section.

As shown in FIG. 1B, the liner 12 has a U-shaped cross section so thatit is closely fitted with the whole U-shaped inner surface of theinclined portion 11a of the chute body 11 except the top flat lid. Theliner 12 is detachably connected at its opposite side edges to theinclined portion 11a by a plurality of fasteners 13 over the length ofthe inclined portion 11a. The liner 12 has a relatively large thickness.As shown in FIG. 1C, the liner 12' has a circular cross section so thatit is attached to the whole circular cylindrical inner surface of theupright portion 11b of the chute body 11.

In the roller mill having the above structure, a feed materialdischarged into the feed inlet chute 10 glides and falls along theliners 12 and 12' mounted on the inner surface of the chute body 11.During the passage of the feed material through the feed inlet chute 10,the liners 12 and 12' formed of a rubber material as a flexible elasticmaterial are elastically deformed by the weight of the feed material andthe gliding/falling forces of the feed material. As the liners 12 and12' thus elastically deformed restore their original forms through anelastic restoring force, the inner surfaces of the liners 12 and 12'generate irregular deformation accompanying peristalsis and vibrationdue to both the weight and the gliding/falling forces of the feedmaterial passing through the feed inlet chute 10 and the elasticrestoring force of the liners 12 and 12'.

Accordingly, even when the feed material to be pulverized contains finepowder having a high viscosity, and a deposit layer of the fine powderis formed on the inner surfaces of the liners 12 and 12' during the passof the feed material through the material inlet chute 10, the depositlayer can soon be removed from the inner surfaces of the liners 12 and12' by the irregular deformation accompanying peristalsis and vibrationmentioned above, thereby preventing the growth of the deposit layer.

In this manner, the removal of the deposit layer formed in the feedinlet chute can be autonomously attained by the deformation of theliners occurring during the passage of the feed material through thefeed inlet chute during the operation of the roller mill. Therefore, theremoval of the deposit layer does not depend on a cleaner or the likemoving in a feed inlet chute as in the conventional roller mill.Further, it is unnecessary to interrupt the operation of the rollermill, so as to perform the removal of the deposit layer. Thus, thegrowth of the deposit layer in the feed inlet chute can be prevented tomake the passage of the feed material smooth and stable. Further, it isunnecessary to unduly largely incline the feed inlet chute for thepurpose of suppressing the deposition of the feed material, and aninclination angle suitable for supplying the feed material to thecentral portion of the rotating table can be selected, thereby effectingefficient pulverization.

Further, the liner formed of a natural or synthetic rubber material ismuch more economical than the ceramic liner or the steel liner with aspecial hard facing of the prior art.

Subsequently, second to fourth preferred embodiments of the presentinvention will be described. The second to fourth preferred embodimentsare similar to the first preferred embodiment but different in themanner of the mounting of the liners in the feed inlet chute and apartial construction of the chute body. Therefore, only an essentialpart primarily including the feed inlet chute is shown in each of thesecond to fourth preferred embodiments. Further, the parts equivalent tothose shown in FIGS. 1A to 1C are denoted by the same reference numeralswith the explanation thereof omitted, and only different parts will beessentially described.

The essential part of a roller mill according to the second preferredembodiment is shown in FIGS. 2A to 2C, wherein FIG. 2A is a verticalsectional view of the essential part; FIG. 2B is a cross section takenalong the line A--A in FIG. 2A; and FIG. 2C is a cross section takenalong the line B--B in FIG. 2A.

As shown in FIG. 2A, a feed inlet chute 20 is of a side feed typesimilar to that in the first preferred embodiment. As shown in FIG. 2B,a U-shaped liner 12 provided inside an inclined portion 21a of a chutebody 21 is uniformly spaced from the U-shaped inner surface of the chutebody 21 except a top flat lid thereof. The liner 12 is detachablyconnected at its opposite side edges through a pair of elongated spacers24 to the inclined portion 21a by a plurality of fasteners 23. Thespacers 24 extend over the length of the inclined portion 21a.

As shown in FIG. 2A, the upper and lower ends of the liner 12 areconnected through a pair of seal members 25 to the inclined portion 21a.Thus, the space between the liner 12 and the inclined portion 21a issealed by the spacers 24 and the seal members 25.

Further, a pair of air vents 21c are provided at the upper and lowerportions of the inclined portion 21a so as to communicate with thesealed space between the liner 12 and the inclined portion 21a. The airvents 21c are connected through pipes (not shown) to an external airsupply device (not shown). With this structure, fine powder contained ina feed material is prevented from entering the space between the liner12 and the inclined portion 21a of the chute body 21. Furthermore, acooling air is supplied from the air supply device into this space tocool the liner 12, thereby preventing the liner 12 from beingdeteriorated by its temperature rise due to hot air introduced into theroller mill.

As shown in FIGS. 2A and 2C, a circular cylindrical liner 12' providedinside an upright portion 21b of the chute body 21 is retained throughan annular spacer 26 to the upright portion 21b in such a manner as tobe suspended from the upper end of the upright portion 21b with anannular space defined between the liner 12' and the upright portion 21b.The wall thickness of the liner 12' inside the upright portion 21b issmaller than that of the liner 12 inside the inclined portion 21a.

Further, as shown in FIG. 2B, three projections 21d serving as spacersare welded to the inner surface of the inclined portion 21a at thebottom portion thereof. The projections 21d are formed as steel rodsextending in parallel over the length of the inclined portion 21a.

In the second preferred embodiment mentioned above, a space is definedbetween the liner 12 and the inclined portion 21a of the chute body 21,and a space is defined between the liner 12' and the upright portion 21bof the chute body 21. In other words, the liners 12 and 12' are notdirectly backed up by the chute body 20 unlike the first preferredembodiment. Accordingly, the liners 12 and 12' can be elasticallydeformed more than those in the first preferred embodiment by the weightand the gliding/falling forces of the feed material passing through thefeed inlet chute 20. As a result, the amplitude of return motion by theelastic restoring force of the liners 12 and 12' can be increased tothereby generate irregular deformation accompanying peristalsis andvibration having a large amplitude on the inner surfaces of the liners12 and 12'. Thus, a deposit layer of fine powder on the inner surfacesof the liners 12 and 12' can be removed more securely.

The provision of the three spacer projections 21d on the inner surfaceof the inclined portion 21a at the bottom portion thereof is intended toprevent that the liner 12 deformed by the feed material passing throughthe chute 20 will come into close contact with the inner surface of theinclined portion 21a at the bottom portion thereof in a wide range togenerate regular deformation on the inner surface in this range.However, if the distance between the liner 12 and the inclined portion21a is set large enough, the spacer projections 21d may be eliminated.

The essential part of a roller mill according to the third preferredembodiment is shown in FIGS. 3A and 3B, wherein FIG. 3A is a verticalsectional view of the essential part; and FIG. 3B is a cross sectiontaken along the line A--A in FIG. 3A.

As shown in FIG. 3A, a feed inlet chute 30 is of a side feed typesimilar to that in the first preferred embodiment. As similar to thesecond preferred embodiment, a U-shaped liner 12 provided inside aninclined portion 31a of a chute body 31 is spaced from the U-shapedinner surface of the inclined portion 31a, and a circular cylindricalliner 12' provided inside an upright portion 31b of the chute body 31 isspaced from the circular cylindrical inner surface of the uprightportion 31b. Further, as also similar to the second preferredembodiment, a pair of air vents 31c are provided at the upper and lowerportions of the inclined portion 31a.

As shown in FIG. 3A, a plurality of push rods 37 are provided so as toextend through the wall of the inclined portion 31a. The push rods 37are spaced at a given pitch in a longitudinal direction of the inclinedportion 31a. As shown in FIG. 3B, each push rod 37 is located at thebottom of the inclined portion 31a in its circumferential direction, andhas a semi-spherical end adapted to push the outer surface of the liner12. Each push rod 37 may be retractably pushed manually in a directfashion by using a hammer or the like or in a remote fashion by using adriving means such as a cylinder 38 (shown by a phantom line in FIG. 3B)or a vibrator connected to the outer end of each push rod 37. Asapparent from FIG. 3B, no spacer projections as used in the secondpreferred embodiment are provided on the inner surface of the inclinedportion 31a of the chute body 31.

In the third preferred embodiment mentioned above, as similar to thesecond preferred embodiment, irregular deformation accompanyingperistalsis and vibration having a large amplitude can be generated onthe inner surfaces of the liners 12 and 12' by the weight and thegliding/falling forces of the feed material passing through the feedinlet chute 30. Moreover, the liner 12 can be forcibly deformed at anarbitrary timing by advancing and retracting each push rod 37. Thus, adeposit layer on the inner surfaces of the liners 12 and 12' can beremoved more securely and easily.

Additionally, similar to the second preferred embodiment, cooling airmay be supplied to the space between the liner 12 and the inclinedportion 31a of the chute body 31 to thereby cool the liner 12.

The essential part of a roller mill according to the fourth preferredembodiment is shown in FIGS. 4A and 4B, wherein FIG. 4A is a verticalsectional view of the essential part, and FIG. 4B is a cross sectiontaken along the line A--A in FIG. 4A.

As shown in FIG. 4A, a feed inlet chute 40 is of a side feed typesimilar to that in the first preferred embodiment. As similar to thesecond and third preferred embodiments, a liner 12 provided inside aninclined portion 41a of a chute body 41 is spaced from the inner surfaceof the inclined portion 41a, and a liner 12' provided inside an uprightportion 41b of the chute body 41 is spaced from the inner surface of theupright portion 31b. Further, similar to the second and third preferredembodiments, a pair of air vents 41c are provided at the upper and lowerportions of the inclined portion 41a.

As shown in FIG. 4A, a plurality of air injection pipes 49 are providedso as to extend through the wall of the inclined portion 41a. The airinjection pipes 49 are spaced at a given pitch in a longitudinaldirection of the inclined portion 41a. As shown in FIG. 4B, the airinjection pipes 49 are arranged in two parallel lines spaced in acircumferential direction of the inclined portion 41a at the bottomportion thereof. Each air injection pipe 49 has a nozzle openingdirected to the inner surface of the liner 12 in close relationshipthereto. Although not shown, the air injection pipes 49 are connectedthrough pipes to a compressed air supply device, so that a pulsatingcompressed air supplied from the compressed air supply device isinjected to the inner surface of the liner 12.

In the fourth preferred embodiment mentioned above, as similar to thesecond preferred embodiment, irregular deformation accompanyingperistalsis and vibration having a large amplitude can be generated onthe inner surfaces of the liners 12 and 12' by the weight and thegliding/falling forces of the feed material passing through the feedinlet chute 40. Moreover, the liner 12 can be forcibly deformed at anarbitrary timing by injecting a pulsating compressed air from each airinjection pipe 49. Thus, a deposit layer on the inner surfaces of theliners 12 and 12' can be removed more securely and easily.

Additionally, the air injected from each air injection pipe 49 isexpelled from the air vents 41c to thereby produce an air flow in thespace between the liner 12 and the inclined portion 41a, thus coolingthe liner 12.

A fifth preferred embodiment of the present invention will now bedescribed with reference to FIG. 5, which shows an essential part of aroller mill and its operation control system according to the fifthpreferred embodiment. The fifth preferred embodiment is similar to thethird preferred embodiment except for the addition of an operationcontrol system for controlling the operation of a feed inlet chute.Therefore, only an essential part primarily including the feed inletchute and the operation control system is shown in FIG. 5. Further, theparts equivalent to those shown in FIGS. 3A and 3B are denoted by thesame reference numerals with the explanation thereof omitted, and onlydifferent parts will be essentially described.

Referring to FIG. 5, reference numeral 30 denotes a feed inlet chutehaving a plurality of push rods 37 similar to those shown in FIGS. 3Aand 3B. A plurality of cylinders 38 are connected to the outer ends ofthe push rods 37, respectively, so as to advance and retract the pushrods 37, thereby forcibly deforming a liner 12. Each cylinder 38 isconnected through a pipe 36 to a compressed air supply device 35, sothat each cylinder 38 is operated by compressed air supplied from thecompressed air supply device 35. A closing valve 36a is provided in thepipe 36. The closing valve 36a is operated by a command from a maincontrol panel 34. The compressed air supply device 35 is also operatedby a command from the main control panel 34.

A pair of pressure detectors 32 are mounted at the upper end portion ofa chute body 31 of the chute 30 outside a housing 1 of the roller milland at the lower end portion of the chute body 31 inside the housing 1,respectively, so as to detect different pressures in the upper and lowerend portions of the chute body 31. Both the pressure detectors 32 areconnected to a differential pressure transmitter 33, which is in turnconnected to the main control panel 34.

In the fifth preferred embodiment mentioned above, the compressed air issupplied to each cylinder 38 by the commands from the main control panel34 to remotely operate each cylinder 38. Accordingly, each push rod 37is advanced and retracted by the corresponding cylinder 38 to forciblydeform the liner 12 as similar to the third preferred embodiment. Thus,a deposit layer on the inner surface of the liner 12 can be removed awaysecurely and easily.

The roller mill is usually operated in the condition where the inside ofthe housing 1 is kept under a negative pressure or a positive pressurewith respect to an atmospheric pressure. Accordingly, when thedeposition of a feed material on the inner surface of the feed inletchute 30 causes a reduction in sectional area of the passage of thechute 30, there results a difference between the pressures at the upperand lower end portions of the chute body 31. According to this preferredembodiment, the pressure difference between the upper and lower endportions of the chute body 31 is detected by the pressure detectors 32during the operation of the roller mill, and the difference between thedetected pressures is transmitted by the differential pressuretransmitter 33 to the main control panel 34. When the pressuredifference reaches a preset value, the main control panel 34 generates acommand to automatically operate each cylinder 38 and accordinglyoperate each push rod 37, thus always maintaining a good condition ofthe chute 30 such that the growth of the deposit layer on the innersurface of the liner 12 is eliminated.

A sixth preferred embodiment of the present invention will now bedescribed with reference to FIG. 6, which shows an essential part of aroller mill and its operation control system according to the sixthpreferred embodiment. The sixth preferred embodiment is similar to thefourth preferred embodiment for the addition of an operation controlsystem for controlling the operation of a feed inlet chute. Therefore,only an essential part primarily including the feed inlet chute and theoperation control system is shown in FIG. 6. Further, the partsequivalent to those shown in FIGS. 4A and 4B are denoted by the samereference numerals with the explanation thereof omitted, and onlydifferent parts will be essentially described.

Referring to FIG. 6, reference numeral 40 denotes a feed inlet chutehaving a plurality of air injection pipes 49 similar to those shown inFIGS. 4A and 4B. The air injection pipes 49 are connected through adistributing header 48 and a pipe 47 to a compressed air supply device46, so that a compressed air supplied from the compressed air supplydevice 46 is injected to a liner 12. A closing valve 47a is provided inthe pipe 47. The closing valve 47a is intermittently operated by acommand from an interval control panel 45.

The interval control panel 45 is connected to a main control panel 44.The main control panel 44 generates a command for controlling intervalsof intermittent operation of the closing valve 47a. That is, the closingvalve 47a is intermittently operated at the intervals based on thecommand from the main control panel 44 through the interval controlpanel 45, thereby generating pulsation of the compressed air suppliedfrom the compressed air supply device 46 and feeding a pulsatingcompressed air thus obtained to each air injection pipe 49.

The compressed air supply device 46 includes an air reservoir tank 51with a pressure transmitter 51a, a compressor 53 connected through apipe 52 having a pressure control valve 52a to the air reservoir tank51, and a pressure controller 50 connected to the pressure transmitter51a and the pressure control valve 52a. The pressure controller 50 isconnected to the main control panel 44. Thus, the pressure of thecompressed air to be supplied to each air injection pipe 49 iscontrolled at a predetermined value by the pressure controller 50 on thebasis of a command from the main control panel 44.

As similar to the fifth preferred embodiment, a pair of pressuredetectors 42 are mounted at the upper and lower end portions of a chutebody 41 of the chute 40, respectively, so as to detect any pressuredifference between the upper and lower end portions of the chute body41. Both the pressure detectors 42 are connected to a differentialpressure transmitter 43, which is in turn connected to the main controlpanel 44.

In the sixth preferred embodiment mentioned above, the pulsatingcompressed air is remotely supplied to each air injection pipe 49 by thecommands from the main control panel 44, and is injected from each airinjection pipe 49 to the liner 12, thereby forcibly deforming the liner12 as similar to the fourth preferred embodiment. Thus, a deposit layeron the inner surface of the liner 12 can be removed securely and easily.Further, as similar to the fourth preferred embodiment, the air injectedfrom each air injection pipe 49 is expelled from air vents 41c formed atthe upper and lower portions of an inclined portion 41a of the chutebody 41 to thereby produce an air flow in the space between the liner 12and the inclined portion 41a, thus cooling the liner 12.

Further, as similar to the fifth preferred embodiment, the pressuredifference in the upper and lower end portions of the chute body 41 isdetected by the pressure detectors 42 during the operation of the rollermill, and the difference between the detected pressures is transmittedby the differential pressure transmitter 43 to the main control panel44. When the pressure difference reaches a preset value, the maincontrol panel 44 generates a command to automatically inject thepulsating compressed air from each air injection pipe 49, thus alwaysmaintaining a good condition of the chute 40 such that the growth of thedeposit layer on the inner surface of the liner 12 is eliminated.

Moreover, the deformation of the liner 12 is not caused by anymechanical means accompanying a sliding motion in this preferredembodiment, thereby greatly reducing wear or the like of the parts ofthe roller mill and effecting easy maintenance. An external forcegenerating the deformation of the liner 12 can be continuously adjustedin value by changing the pressure of the compressed air to be supplied,and also can be arbitrarily changed by controlling the intervals of thepulsation of the compressed air. Thus, the external force can be variedwidely and immediately in response to a change in characteristics of afeed material.

Although the liners 12 and 12' are formed of a natural or syntheticrubber material in the first to sixth preferred embodiments mentionedabove, the material of the liners 12 and 12' is not limited to the abovein the present invention. In particular, when there is defined a spacebetween each liner and the chute body as in the second to sixthpreferred embodiments, a metal plate or the like having a flexibilityand an elasticity may be used for each liner. Also in this case, asimilar effect can be obtained.

Further, in the fifth and sixth preferred embodiments, the two pressuredetectors are mounted at the upper and lower end portions of the chutebody, respectively, and the operation of the push rods and the airinjection pipes is controlled according to the difference between thepressures detected by the pressure detectors. However, it is not alwaysnecessary to mount the two pressure detectors at the upper and lower endportions. For example, a single pressure detector may be mounted at theupper end portion only of the chute body to detect a change in internalpressure of the chute body, from which the growth of the deposit layerin the chute may be determined. Also in this case, similar operationcontrol can be effected.

While the invention has been described with reference to specificembodiments, the description is illustrative and is not to be construedas limiting the scope of the invention. Various modifications andchanges may occur to those skilled in the art without departing from thespirit and scope of the invention as defined by the appended claims.

What is claimed is:
 1. A roller mill comprising:a housing; a millingtable adapted to be rotated about a vertical axis provided in saidhousing; a plurality of milling rollers provided in said housing andmounted so as to act against an outer portion of the upper surface ofsaid milling table; and a feed inlet chute extending obliquely through aside wall of said housing for supplying a feed material from outside thehousing onto said milling table to be pulverized between said millingtable and said milling rollers; wherein said feed inlet chute comprisesa liner made of a flexible elastic material, and a chute body such thatsaid liner is mounted inside said chute body; wherein said roller millfurther comprises liner deforming means for forcibly deforming saidliner; and said feed inlet chute further comprises a plurality ofspacers mounted between said chute body and said liner to thereby definea space between said liner and said chute body.
 2. The roller millaccording to claim 1, further comprising pressure detecting means fordetecting the pressure in said feed inlet chute; andcontrolling meansfor operating said liner deforming means in accordance with the pressuredetected by said pressure detecting means.
 3. The roller mill accordingto claim 2, further comprising cooling means for cooling said liner. 4.The roller mill according to claim 2, wherein said liner deforming meanscomprises a push rod adapted to be pushed against and retracted fromsaid liner and a hydraulic cylinder for operating said push rod whereinsaid cylinder is controlled by said controlling means in accordance withthe pressure detected by said pressure sensors.
 5. The roller millaccording to claim 2, wherein said liner deforming means comprises acompressed air supply unit and an air injection pipe adapted to injectpulses of compressed air supplied by said air supply unit towards saidliner wherein the supply of air from said air supply unit to saidinjection pipe is controlled by said controlling means in accordancewith the pressure detected by the pressure detecting means.
 6. Theroller mill according to claim 2, wherein said pressure detecting meanscomprises a first pressure sensor for detecting the pressure at theupper portion of said feed inlet chute and a second pressure sensor fordetecting the pressure at the lower portion of said feed inlet chute andwherein the controlling means operates said liner deforming means inaccordance with the difference in pressures detected by the firstpressure sensor and second pressure sensor.
 7. The roller mill accordingto claim 1, further comprising cooling means for cooling said liner. 8.The roller mill according to claim 1, wherein said liner is detachablyconnected to said chute body by a fastener.
 9. The roller mill accordingto claim 1, wherein said liner is closely fitted to the inner surface ofsaid chute body.
 10. The roller mill according to claim 1, wherein saidliner deforming means comprises a push rod adapted to be pushed againstand retracted from said liner.
 11. The roller mill according to claim 1,wherein said liner deforming means comprises an air injection pipeadapted to inject pulses of compressed air towards said liner.
 12. Theroller mill according to claim 1, wherein said liner is made from arubber material.
 13. The roller mill according to claim 1, wherein saidfeed inlet chute further comprises projections on an inner surface ofsaid chute body and wherein said projections contact said liner.
 14. Aroller mill comprising:a housing; a milling table adapted to be rotatedabout a vertical axis provided in said housing; a plurality of millingrollers provided in said housing and mounted so as to act against anouter portion of the upper surface of said milling table; and a feedinlet chute extending obliquely through a side wall of said housing forsupplying a feed material from outside the housing onto said millingtable to be pulverized between said milling table and said millingrollers; wherein said feet inlet chute comprises:a liner made of aflexible elastic material; a chute body such that said liner is mountedinside said chute body; and attachment means at each longitudinal end ofsaid liner for attaching said liner to said chute body, wherein a spaceis defined between said liner and said chute body which extendssubstantially over a full length of said liner and said chute body topermit a deformation of said liner within said space as the feedmaterial is supplied through said feed inlet chute for preventing anadherence of the feed material on the liner.
 15. The roller millaccording to claim 14, wherein said feed inlet chute further comprises aplurality of spacers mounted between said chute body and said liner.